Aromatic polyimide is known as a resin with excellent heat resistance and mechanical properties U.S. Pat. No. 3,179,631, U.S. Pat. No. 3,249,588 and U.S. Pat. No. 4,755,555), and it is widely used in jet engines, business equipment, and automobile parts. Nevertheless, there is a tendency toward restriction of its use because many polyimides are difficult to mold. In particular, many polyimides are molded into the desired shape, such as films, etc., before the polyamide acid, which is a precursor to polyimide, changes to polyimide, or are molded from a molded article of polyimide into the desired shape by machine molding.
Therefore, there is a need for an injection-moldable polyimide resin composition. In order to solve this invention, a polyimide polymer mixture is disclosed (U.S. Pat. No. 5,470,922, which is incorporated herein by reference) that is made from at least one polymer that can be melted and molded at a temperature lower than 400.degree. C. and that is selected from polyamide and polyester, preferably polyamide or polyester in the form of a liquid crystal polymer, and polyamide acid. This polyimide polymer mixture has heat resistance and mechanical properties rivaling those of conventional aromatic polyimide and excellent injection molding performance.
Nevertheless, because polyamide acid is used to produce this polymer mixture, a process for producing polyamide acid is needed. Therefore, simplification of the manufacturing process is needed. This invention presents a new method of producing an injection-moldable polyimide resin composition with better mechanical properties by a simpler manufacturing method.